Method and apparatus for measuring the quantity of a liquid in a vehicle container

ABSTRACT

Apparatus and method for measuring the volume of a liquid in a fuel tank in a vehicle subject to varying external forces caused by movement or changes in the roll and pitch angles of the vehicle wherein the tank is mounted to the vehicle and subject to forces along the yaw axis of the vehicle. One or more tank load cells provides an output proportionally representing the load thereon. The load cells are placed between a portion of the tank and a portion of a reference surface of the vehicle and are sensitive along an axis that is substantially normal to the mounting surface and generally parallel to the yaw axis of the vehicle. A processor executes a derived relationship between the load cell output and the volume of fuel in the tank so as to convert the output signal from the load cell into output information representative of the volume of the fuel in the tank.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 08/819,609 filed Mar. 17, 1997, now U.S. Pat. No.6,615,656, which is a continuation-in-part of U.S. patent applicationSer. No. 08/239,977 filed May 9, 1994, now abandoned, which areincorporated by reference herein in their entirety.

[0002] This application claims priority under 35 U.S.C. §119(e) of U.S.provisional patent application Ser. No. 60/461,648 filed Apr. 9, 2003.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] This invention concerns an improved system for determining thequantity of a fluid stored in a container subject to varying externalforces, and particularly to the quantity of gasoline stored in anautomobile gas tank.

[0005] 2. Description of the Related Art

[0006] The present invention is an improvement on the inventiondisclosed in U.S. Pat. No. 05,133,212 to Grills et al., the contents ofwhich are included herein by reference. Grills et al. disclose aweighing system utilizing a plurality of load cells supporting the fueltank and a reference weight and load cell which, in combination with thetank load cells, corrects automatically for the external forces actingon the tank to give an accurate average measure of the quantity ofliquid in the tank. Although this system is quite accurate and finds itsbest use where the cost of such a system can be justified, such as inmeasuring the quantity of fuel in an airplane fuel tank, the complexityof such a system is not justified where cost is of relatively greaterimportance such as in the determination of the amount of fuel in anautomotive fuel tank.

[0007] Another tank weighing system which does not use load cells isdisclosed by Kitagawa et al. in U.S. Pat. No. 04,562,732 where the tankis supported on one side by a torsion bar system. In contrast to Grillset al., although the Kitagawa et al. device is quite complicated andconsequently quite expensive, it contains no system for correcting forthe roll or pitch motions of the vehicle other than to average the tankreadings over an extended period of time.

[0008] The external forces acting on an automobile fuel tank due toturning, roll and pitch although significant are much less severe in anautomobile than in an airplane. Forces due to pitch generally arise whena vehicle is climbing or descending a hill which in North America rarelyexceeds 15 degrees and only occasionally exceeds 5 degrees. Roll anglesof more than 5 degrees are similarly uncommon. Even when steep anglesare encountered, it is usually only for a short time. This is notgenerally the case in aircraft, especially high performance militaryaircraft, where turning pitch and roll related forces are not onlygreater in magnitude but can last for an extended period of time.

[0009] The most common systems of measuring the quantity of fuel in anautomobile fuel tank use a variable resistance rheostat which iscontrolled by a float within the gas tank. This system makes no attemptto correct for external forces acting on the tank or for the angle ofthe vehicle. Modern gas tanks have a convoluted shape and the level offuel is frequently a poor indicator of the amount of fuel within thetank. In many implementations, for example, the gage continues toregister full even after several gallons have been consumed. Similarly,the gage will usually register empty when there are several gallonsremaining. It is then a guessing game for the driver to know how far hecan go before running out of gas.

[0010] The problem has been compounded with the implementation of adigital fuel gage display where the driver now gets an inaccuratedisplay, with seemingly great precision, of the amount of fuel used andamount remaining in the tank. If, for example, the gage states that 14.5gallons have been consumed and the driver has the tank filled andnotices that it takes 15.3 gallons to fill it he wonders if he is beingcheated by the service station or, as a minimum, he begins to doubt theaccuracy of the other gages on the instrument panel. The inaccuracy ofthe fuel gage is now a common complaint received by at least one vehiclemanufacturer from its customers. Similar but less severe problems occurwith other fluid containers or reservoirs on a vehicle.

[0011] These prior art float systems are also vulnerable to errors dueto fouling of the resistor induced by the necessity to operate thesensing elements in direct contact with the mixture held in the tank.These errors can cause the system to become inoperative or to change itscalibration over time. These and other problems associated with theprior art fuel gages are solved by the present invention as disclosedbelow.

[0012] Reference is also made to U.S. Pat. No. 04,890,491 (Vetter etal.) which describes a system for indicating the level of fuel in anautomobile tank (FIG. 4) which includes a fuel level detector 1, adetector 24 for detecting the longitudinal inclination of the vehicle, adetector 25 for detecting the transverse inclination of the vehicle anda microcomputer 26 containing a table providing an “immersioncharacteristic curve”. In operation, the microcomputer 26 receives inputfrom the fuel level detector 1 and inclination detectors 24, 25 andcorrects the level of fuel as measured by the fuel level detector 1 inlight of the transverse and longitudinal inclination of the vehicle asmeasured by the detectors 24,25 by the application of the immersioncharacteristic curve to avoid false readings caused by inclination ofthe vehicle (Col. 6, lines 9-22). Vetter et al. does not take anyreadings during periods of inclination of the vehicle during operationthereof nor provide a corrected level of liquid.

[0013] Reference is also made to U.S. Pat. No. 04,815,323 (Ellinger etal.) which describes a fuel quantity measuring system having ultrasonictransducers for measuring volume of fuel in a tank. In the embodimentshown in FIG. 1 (but not the embodiment shown in FIG. 2), the systemincludes ultrasonic tank sensor units which provide a signalrepresentative of the round-trip time between each sensor to the surfaceof the fuel, a processor unit (CPU) which receives the round-trip time(which is proportional to the height level of fuel in the tank) and adisplay to display the volume of fuel in the tank. In this embodiment,the processor is described as performing height-volume calculations andthen correcting for attitude, i.e., the pitch and roll of the vehicle(Col. 2, line 67 to Col. 3, line 2). As such, it is clear that for thisembodiment, the measured round-trip time is applied to the height-volumetable to obtain a volume corresponding to that round-trip time. Thisvolume estimation is thereafter corrected based on the attitude, i.e.,the measured pitch and roll (see, e.g., Col. 3, lines 14-16, 24-35).Note that rather inaccurate attitude gages are used and there is nomention of the use of an inertial measurement unit (IMU) or otheraccurate angular measurement system. An IMU usually contains threeaccelerometers and three gyroscopes. The errors in an IMU can becorrected if GPS or other absolute data is available through the use ofa Kalman Filter as discussed in the current assignee's U.S. provisionalpatent application Ser. No. 60/461,648 (Attorney Docket No. ATI-353PRO).

[0014] In the embodiment in Ellinger et al. FIG. 3, the tank 12 includesthree ultrasonic transducers 14,16,18 which send a respective signalrepresentative of the round-trip time to the surface of the fuel 10 in arespective stillwell 22 each surrounding that transducer to a computer28 through a multiplexer 34. Only one transducer is related to fuellevel (see FIG. 2) and the other two transducers are related toreference purposes and fuel density. The computer 28 has a memory 30which it appears contains height-volume tables specific to each locationof the transducer (See Col. 5, lines 29-31) so that the measuredround-trip time representative of the height level of fuel at thatsensor location can be converted into a volume measurement. Thus, inthis Ellinger et al. embodiment, the height of the level of fuel in thetank at each different location is converted to a volume measurementbased on the height-volume tables. However, in this embodiment, there isno disclosure of the converted volume measurements being corrected by anattitude correction factor, i.e., the pitch and roll angles of thevehicle.

[0015] In an attempt to gain accuracy, prior art systems use frequentlymultiple fluid level measuring transducers or pitch and/or roll anglemeasurement devices. Future vehicles are expected to come equipped withan accurate IMU that is expected to be at least an order of magnitudemore accurate than the mentioned attitude measurement devices. Theinformation from the IMU should be generally available on a vehicle busand therefore it can be used with the liquid level systems at nosignificant additional cost. This will permit the use of a single levelmeasuring device and still result in greater accuracy than heretoforeavailable.

[0016] Also, there is not believed to be anything in the prior art citedabove that suggests the use of wireless transducers for levelmeasurement such as devices based on surface acoustic wave technology(SAW). If the vehicle has a SAW-based tire pressure monitor, then to addadditional devices is not only very inexpensive but reduces the numberof wires that need to be placed in a vehicle further reducing costs andimproving reliability.

OBJECTS AND SUMMARY OF THE INVENTION

[0017] The fluid level gage of the present invention uses a combinationof (i) one or more load cells or fuel level measuring devices, plus insome cases other sensors which measure the pitch or roll angle of thevehicle or the fuel density, to approximately measure the quantity ofthe liquid in a tank and (ii) a processor and algorithm to correct forthe inaccuracies arising from the pitch and roll angles of the vehicle,other external forces or from variations in fuel density. Althoughseveral weighing systems are disclosed for illustrative purposes, theinvention applies to any method of making an approximate measurement ofthe fuel quantity and then using analytical techniques to improve on themeasurement.

[0018] The principle objects of this invention are:

[0019] 1. to provide a measuring system for determining the quantity ofliquid in a reservoir of an automotive vehicle operating on land that issubject to accelerations and pitch and roll rotations.

[0020] 2. To provide analytical methods using a processor and algorithmand the output from one or more transducers for accurately determiningthe quantity of liquid in an automobile reservoir when the reservoir hasa complicated geometry.

[0021] 3. To provide a simple, low cost system using a capacitance witha liquid as a dielectric to determine the level of the liquid in thereservoir.

[0022] 4. To provide for a simple correction for the effects of pitchand roll in a reservoir liquid level measurement system through the useof an empirically or analytically derived relationship between theindividual transducer readings and the quantity of liquid in thereservoir.

[0023] 5. To provide for a correction for the effects of pitch and rollthrough the use of pitch and roll angle sensors, and particularly anIMU, and an empirically or analytically derived relationship betweentransducer readings and the quantity of liquid in the reservoir.

[0024] 6. To eliminate the errors on automobile tank weighing systemscaused by the accumulation of mud or ice on an exposed tank.

[0025] 7. To eliminate the errors on automobile tank weighing systemscaused by the variations in fuel density.

[0026] 8. To provide a variety of low cost load cell designs for use intank weighing or pressure measuring systems.

[0027] 9. To provide a method of increasing the accuracy of thecurrently used float fuel gages.

[0028] 10. To provide for a more accurate liquid level gage.

[0029] 11. To provide for a wireless transmission of liquid levelmeasurement transducers information to an interrogator.

[0030] 12. To provide for a transducer used in determining the level ofa liquid in a reservoir that does not require power to be supplied bythe vehicle power system or a battery.

[0031] Among the believed novel aspects embodied in the presentinvention is that a system, constructed in accord with the presentinvention, can use a variety of different liquid level measuringtransducers which by themselves give an inaccurate measurement of thequantity of a liquid in a reservoir but when combined with anempirically derived algorithm results in a highly accurate liquidquantity measurement system. These transducers can be weight measuringload cells, vehicle angle measuring transducers, or liquid levelmeasuring devices based on either float, ultrasonic or capacitivemeasurement technologies.

[0032] When load cells are used they are aligned to be sensitivegenerally parallel along an axis substantially normal to a horizontalplane and generally parallel to the yaw or vertical axis of the vehicle.A microprocessor with analog-to-digital converters converts the analogsignals into output information representative of the volume or level ofthe liquid in the reservoir by a variety of techniques but all employingthe use of an algorithm which is based on empirical or analyticalapproximation techniques to relate the quantity of liquid in thereservoir to the measured quantities.

[0033] Although a number of the systems disclosed and illustrated belowmake use of a number of weight measuring devices for illustration, theinvention is not the use of weighing per se but the use of one or moreof a variety of transducers including load cells, angle gages, IMU, andlevel gages in combination with an algorithm and processor to determinethe quantity of liquid in the reservoir with greater accuracy than canbe obtained from a single transducer alone.

[0034] In addition, in order to achieve one or more of the aboveobjects, an apparatus for measuring the volume of a liquid in a fueltank in a vehicle subject to varying external forces caused by movementor changes in the roll and pitch angles of the vehicle includes a fueltank mounted to the vehicle and subject to forces along the yaw axis ofthe vehicle and a plurality of SAW pressure sensors mounted on the tankwhereby each SAW pressure sensors provides an output signalrepresentative of pressure applied thereto by material in an interior ofthe tank (the fuel or air). A processor or other computational device iscoupled to the SAW pressure sensors and receiving the output signalstherefrom and processes the output signals to obtain a volume of fuel inthe tank. More specifically, the processor is associated with a memoryunit that stores an algorithm representative of a derived relationshipbetween the parameters corresponding to the output signals from the SAWpressure sensors and the volume of fuel in the tank and applies thealgorithm using the instantaneous output signals from the SAW pressuresensors as input to obtain the volume of fuel in the tank. The algorithmmay be obtained by conducting a plurality of measurements, eachincluding the known volume of the tank and output signals from the SAWpressure sensors for that known volume of fuel in the tank.

[0035] In enhanced embodiments, the plurality of SAW pressure sensorsinclude a number of SAW pressure sensors arranged each at a differentlocation on a bottom of the tank and a SAW pressure sensor arranged at atop of the tank. The algorithm considers output signals from the SAWpressure sensor arranged at a top of the tank to eliminate effects ofvapor pressure within the tank. The algorithm may be a neural network.

[0036] In another embodiment, a fluid storage tank for a vehicle subjectto varying external forces caused by movement or changes in the roll andpitch angles of the vehicle in accordance with the invention includes acontainer having a sidewall defining in part an interior and a SAWsensor arranged on the sidewall and including a pressure sensor arrangedon an inside of the container and a temperature sensor arranged on anoutside of the container. The pressure sensor measures deflection of thesidewall and the temperature sensor measures temperature of the fluid.Pressure and temperature readings from the tank may thus be obtained ina wireless and powerless manner.

[0037] Another disclosed method for measuring the volume of a liquid ina fuel tank in a vehicle subject to varying external forces caused bymovement or changes in the roll and pitch angles of the vehicle entailsconducting a plurality of measurements, each measurement including theknown volume of the tank and the value of at least three parametersconcerning the tank, at least one of the parameters being the pitch orroll angle of the vehicle as determined by an inertial measurement unit(IMU), generating an algorithm from the plurality of measurements fordetermining the volume of fuel in the tank upon the receipt of currentvalues of the parameters, inputting the algorithm into a processorarranged in connection with the vehicle, measuring the parameters duringoperation of the vehicle, and inputting the measured parameters into thealgorithm in the processor means whereby the algorithm provides thevolume of fuel in the tank. Aside from the pitch and/or roll angle, theremaining parameters may be the load of the tank on a load cell arrangedat a first location, the load of the tank on a load cell arranged at asecond location, the load of the tank at a load cell arranged at a thirdlocation, the height of the fuel at a first location in the tank, theheight of the fuel at a second location in the tank and the height ofthe fuel at a third location in the tank.

[0038] The novel features of construction and operation of the inventionwill be more clearly apparent during the course of the followingdescription referencing the accompanying drawings where a few preferredforms of the device of the invention are illustrated and wherein likecharacters of reference designate like parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The following drawings are illustrative of embodiments of theinvention and are not meant to limit the scope of the invention asencompassed by the claims.

[0040]FIG. 1 is an idealized schematic showing a system in accordancewith the present invention using load cell transducers.

[0041]FIG. 2 is a perspective view of an automobile fuel tank supportedby three load cells shown prior to attachment to the tank and usingthree analog to digital converters shown schematically.

[0042]FIG. 3 is a detailed view of a four element strain gage prior tomounting to a metal beam to form a load cell.

[0043]FIG. 4 is a perspective view of an automobile fuel tank supportedby three load cells shown prior to attachment to the tank as in FIG. 2but using only one analog to digital converter shown schematically.

[0044]FIG. 5 is a perspective view of an automobile fuel tank supportedby three load cells shown prior to attachment to the tank as in FIG. 4using one analog to digital converter for the three load cells and alsousing pitch and roll angle sensors with associated analog to digitalconverters shown schematically.

[0045]FIG. 6 is a perspective view of an automobile fuel tank supportedby two load cells shown prior to attachment to the tank and using twoanalog to digital converters shown schematically.

[0046]FIG. 7 is a perspective view of an automobile fuel tank supportedby two load cells shown prior to attachment to the tank and using twoanalog to digital converters shown schematically as in FIG. 6 but withadditional pitch and roll angle sensors with their associated analog todigital converters shown schematically.

[0047]FIG. 8 is a perspective view of an automobile fuel tank supportedby one load cell shown prior to attachment to the tank and using oneanalog to digital converter shown schematically with additional hingesupports for the fuel tank and pitch and roll sensors shownschematically mounted separate from the tank and each having two analogto digital converters.

[0048]FIG. 9 is a perspective view of the apparatus as in FIG. 2 withthe addition of a protective skirt under the tank to prevent the buildupof mud and ice on the tank.

[0049]FIG. 10 is a perspective view of the apparatus as in FIG. 2 withthe addition of a specific gravity measuring system comprising a massand load cell with its associated analog to digital converter.

[0050]FIG. 11 is a perspective view of a cantilevered beam type loadcell for use with the fuel gage system of this invention.

[0051]FIG. 11A is a planar cross section view with parts cutaway andremoved of the load cell of FIG. 11 shown mounted onto the vehiclefloor-pan and attached to the fuel tank.

[0052]FIG. 12 is a perspective view of a simply supported beam type loadcell for use with the fuel gage system of this invention.

[0053]FIG. 12A is a planar cross section view with parts cutaway andremoved of the load cell of FIG. 12 shown mounted onto the vehiclefloor-pan and attached to the fuel tank.

[0054]FIG. 13 is a perspective view of a tubular load cell for use withthe fuel gage system of this invention.

[0055]FIG. 13A is a planar cross section view with parts cutaway andremoved of the load cell of FIG. 13 shown mounted onto the vehiclefloor-pan and attached to the fuel tank.

[0056]FIG. 14 is a perspective view of a torsional beam load cell foruse with the fuel gage system of this invention.

[0057]FIG. 14A is a planar cross section view with parts cutaway andremoved of the load cell of FIG. 14 shown mounted onto the vehiclefloor-pan and attached to the fuel tank.

[0058]FIG. 15 is a perspective view with portions cut away of anautomobile fuel tank supported by one load cell, located at theapproximate center of gravity of the fuel tank when full, shown beforeattachment to the tank and using one analog to digital converter shownschematically with additional lateral supports for the fuel tank.

[0059]FIG. 16 is a perspective view with portions cut away of anautomobile fuel tank with a conventional float and variable resistormechanism used in combination with pitch and roll angle measuringtransducers and associated analog to digital converters and associatedelectronic circuitry.

[0060]FIG. 17 is a perspective view with portions cut away of anautomobile fuel tank with a rod-in-tube capacitive fuel level measuringdevice used in combination with pitch and roll angle measuringtransducers and associated analog to digital converters and electroniccircuitry shown schematically.

[0061]FIG. 17A is a cross-section view with portions cutaway and removedof the rod-in-tube capacitor fuel level measuring device of FIG. 17.

[0062]FIG. 18 is a perspective view with portions cut away of anautomobile fuel tank with a parallel plate capacitive fuel levelmeasuring device, where the plates are integral with the top and bottomof the fuel tank, used in combination with pitch and roll anglemeasuring transducers and associated analog to digital converters andelectronic circuitry shown schematically.

[0063]FIG. 18A is a circuit diagram showing the capacitance circuitbetween the plates of the capacitor of FIG. 18 illustrating a source oferrors caused by a shunt capacitance to the earth.

[0064]FIG. 19 is a perspective view with portions cut away of anautomobile fuel tank with an ultrasonic fuel level measuring devicelocated at the bottom of the tank, used in combination with pitch androll angle measuring transducers and associated analog to digitalconverters and electronic circuitry shown schematically.

[0065]FIG. 19A is similar to FIG. 19 but includes a plurality ofultrasonic transducers

[0066]FIG. 20 is a partial cutaway view of a section of a fluidreservoir with a SAW fluid pressure and temperature sensor formonitoring fuel, oil, water or other fluid pressure.

[0067]FIG. 21 is a perspective view with portions cutaway of a SAW-basedvehicle fuel gage.

[0068]FIG. 21A is a top detailed view of a SAW pressure and temperaturemonitor for use in the system of FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] Referring now to the drawings wherein like reference numeralsrefer to the same or similar elements, FIG. 1 illustrates, in anidealized schematic form, an apparatus 10 constructed in accordance withone implementation of the present invention for use in measuring thevolume or level of fuel 12 in a fuel tank 14 that is subject to changingexternal forces caused by movement or changes in the pitch or rollangles of tank 14. Instead of a tank, any type of fluid reservoir can beused in accordance with the invention and therefore the term “tank” willrefer to any type of reservoir or receptacle which stores a fluid.

[0070] At least one, and preferably a plurality, of tank strain gageload cells 16 are provided for tank 14, as described below. These straingage load cells 16 normally operate in either compression or tensionmode in response to external load forces acting on the cell inconjunction with an applied direct current voltage to provide analogvoltage outputs that correspond, in known proportion, to the load forcesapplied to each load cell 16. Alternately, a SAW-based load cell can beused where the strain on the strain sensing element results in a changein the natural frequency of the SAW device or a change in the time delaybetween the reception and retransmission of an RF interrogating pulse.For a more detailed explanation, reference is made to U.S. provisionalpatent application Ser. No. 60/461,648 and related non-provisionalpatent application Ser. No. ______ (designated Attorney Docket No.ATI-353) which are incorporated herein by reference. In someimplementations of the SAW load cell, power and information wires do notneed be attached to the SAW device and the device becomes both wirelessand powerless (i.e., does not require power via wires).

[0071] Tank load cells 16 are placed between different portions ofcontainment tank 14 and a solid or rigid portion of a common referencesurface, normally a substantially horizontal surface such as thefloor-pan 18 of the vehicle, which, in the preferred embodiment, is anautomotive land vehicle. Load cells 16 are aligned to be sensitive toload forces generally parallel along an axis 20 that is substantiallynormal to the common reference surface 18. In most instances, the axis20 will be parallel to a vertical axis, or to an axis that is normal tothe axis of usual forward motion of the tank or vehicle. As an example,in an automobile, tank load cells 16 will normally be placed so as to besensitive along the yaw or vertical axis of the automobile.

[0072] Referring once again to FIG. 1, a device 28 retains datadescriptive of the known tank empty weight for use as better describedbelow in determining the level of liquid in the tank. Devices for thisdata retention for use with systems employing a processor may include aRandom Access Memory or Read-Only Memory device, operatively coupledwith the processing unit in the usual fashion that include datarepresenting the known tank empty weight.

[0073] A computational device 30, such as a processing unit (or anequivalent circuit formed from a coupled series of operationalamplifiers as illustrated in FIG. 2 of the above referenced patentnumber U.S. Pat. No. 05,133,212), is connected to receive the analogvoltage outputs from load cells 16 and pitch and roll angle sensor 24,and converts these analog signals, essentially simultaneously, intooutput information of the volume of the liquid in the fuel tank. Theplurality of tank load cell outputs are summed, in one implementation ofthis invention, to form a tank gage sum signal from which is subtractedthe known tank empty weight to form a tank net weight signal. Thissignal is then used to generate a liquid volume signal based on knownweight volume relationships.

[0074] The preferred embodiment of a system in accord with the presentinvention would further include means for averaging out short termtransients appearing in the analog voltage output signals from the loadcells as a result of inertial forces caused by the contents of the tank.This would eliminate measurement errors caused by “sloshing” of theliquid in the tank due to short term or violent movements of the tankitself and the inertia inherent in a dynamically moving containedliquid. Such averaging means are most easily accommodated within theprocessing unit through the use of a computer algorithm, however, itcould also be accommodated using appropriate electrical circuitryoperating on the analog signals.

[0075] Finally, to present the signal representing the volume or levelof the liquid in the tank to an observer, it is preferred that at leastone tank liquid level readout device 34, such as a dial, LCD or LEDdisplay, be operatively linked to computational device 30 for displayingthe volume and/or level of the liquid contained in the tank. This devicemay also record this data for readout at a later date, or store theinformation for use by other devices. In many implementations, thelinkage between the display device 34 and the computational unit ormicroprocessor 30 is through a second processing unit 32 which controlsthe instrument panel displays and is sometimes called an instrumentpanel computer.

[0076] In the embodiment of FIG. 1, processor 30 also contains one ormore devices for the conversion of the analog voltage output signalsfrom the load cells and angle sensors or gages to digital form forfurther processing in a processing unit. Accordingly, this preferredembodiment would require one or more analog-to-digital converters (ADCs)which, in any of the usual ways, converts the analog voltage signaloutputs from the load cells and angle gages into digital signals forprocessing by the computational device of the system. In mostmicroprocessor implementations, multiple ADCs are accomplished by usinga single ADC combined with a multiplexing circuit which cyclicallyswitches the ADC to different inputs. Thus when referring to multipleADCs below, this will mean either the actual use of multiple single ADCunits or one ADC in combination with a multiplexing circuit. Othercircuits are used in the SAW implementation of this invention asexplained in the '648 provisional patent application.

[0077] The present invention also includes a method for measuring thequantity of a fuel in a fuel tank subject to varying external forcescaused by movement or changes in the pitch or roll angles of the tank.This method includes the steps of:

[0078] a) mounting a fuel tank to the vehicle so that it is movablealong the yaw or vertical axis of the vehicle;

[0079] b) providing at least one analog signal in proportionrespectively to the load on at least one tank load cell, each cell beingmounted or placed between a portion of the fuel tank and a portion of areference surface of the vehicle, and each cell being sensitive along anaxis substantially normal to the reference surface and generallyparallel to the yaw axis of the vehicle;

[0080] c) providing signals proportionally representing the pitch orroll angles of the vehicle; and,

[0081] d) converting the analog load cell signal and the pitch and rollangle signals into output information representative of the volume ofthe liquid in the fuel tank by, in some embodiments, converting theanalog load cell signal to a digital signal and inputting the digitalsignal and the pitch and roll signals into a processor having analgorithm, the algorithm using (i) the inputted load cell signal and thepitch and roll signals independently (ii) with a derived relationshipbetween the signals and the fuel volume to output the fuel volumeinformation.

[0082] In general, the algorithm used in this method can take the formof a look-up table where intermediate fuel volumes are derived byinterpolation from the recorded values in the table, or of an equationwhich is an approximation to empirical test results. Alternately, andmost preferably, the algorithm can be in the form of a neural network orfuzzy logic system, or other pattern recognition system, which caneither be software or hardware based. The neural network is trained byconducting a series of tests measuring the load on the tank load cellsand associated these measured loads with the known volume of fuel in thetank. After a significant number of tests are conducted, the data isinput into a pattern recognition algorithm generating program togenerate a neural network. In use, it is possible to provide the neuralnetwork with the readings on the load cells and obtain therefrom anaccurate indication of the volume of fuel in the tank.

[0083] In FIG. 2, a perspective view of an automobile fuel tanksupported by three load cells is shown prior to attachment of the loadcells to the tank. In this configuration, three analog to digitalconverters, shown schematically, are used. For the purposes ofillustration, the load cells are shown as the cantilevered beam-typeload cells. Other geometries, as described below, such as simplysupported beam or tubular load cells could be used. In the devicedisclosed in the above referenced Grills et al. patent, the load cellsignals are summed to create a single signal which is proportional tothe entire weight of the fuel tank. In contrast, in the device shown inFIG. 2, each load cell signal is individually digitized and analyzed. Inthis regard, a neural network can be trained to convert values fromthese three load cells to an indication of the volume of fuel in thetank, i.e., by conducting tests measuring the load on each cell fornumerous different known volumes of fuel in the tank and then inputtingthis data into a pattern recognition algorithm generating program.

[0084] When the fuel tank is tilted through a rotation about either thepitch or roll axes, the load cells will no longer measure the trueweight of the fuel but will instead measure the component of the weightalong the axis perpendicular to the fuel tank horizontal plane or thevehicle yaw axis. Compensation for this error is achieved in the abovereferenced Grills et al. patent through the use of a separate referencemass and load cell. In contrast, in the invention as illustrated in FIG.2, a measure of the tank rotation is achieved by analyzing theindividual load cell readings rather than summing them as done in theGrills patent. If used, the neural network can be trained on datarepresenting the fuel tank at different inclinations, which woulddirectly affect the readings of the load cells. As such, the neuralnetwork would still provide an accurate indication of the fuel volume inthe tank in spite of the inclination of the tank during use. In thisregard, it should be mentioned that the neural network can be trained onany three items of information concerning the fuel tank, i.e., threeparameters from the following: the load at a first load cell, the loadat a second fuel cell, the load at a third fuel cell, the angularrotation about the pitch axis and the angular rotation about the yawaxis. With the knowledge of any of these three parameters, the neuralnetwork can accurately provide the volume of fuel in the tank (providedit is trained accordingly).

[0085] The tank and weighing system is shown generally at 200 in FIG. 2.Cantilevered load cells 202, 204 and 206 are mounted to the floor-pan ofan automobile, not shown, through the use of appropriate mountinghardware and mounting holes 221, 223 and 225 respectively. The loadcells similarly are mounted to the fuel tank using mounting hardware,not shown, through mounting holes 222, 224 and 226 and through flexibleattachment grommets 203, 205 and 207. The weight of the fuel tank 210causes cantilevered beams 202, 204 and 206 to bend. The amount of thisbending is related to the weight of the fuel tank and fuel therein asexplained in more detail below. The cantilevered beam load cells 202,204 and 206 are shown schematically connected to the fuel gageelectronic package 250 by means of wires 232, 234 and 236 respectively.In particular, the outputs of load cells 202, 204 and 206 are inputs toanalog-to-digital ADCs 252, 254 and 256 respectively.

[0086] In the system illustrated in FIG. 2, the heavy portion of thefuel tank, that is the portion which contains the greater amount of fuelwhen the fuel tank is full, is toward the rear of the vehicle and issupported by load cells 204 and 206. Similarly the lighter portion ofthe fuel tank is more forward in the vehicle and is supported by loadcell 202. Hole 290 is provided in the heavier portion of the fuel tankto receive the fuel pump. Another hole, not shown, also exists generallyfor filling the tank. The particular tank shown in FIG. 2 is made fromtwo metal stampings and joined at lip 295 by welding.

[0087] If the vehicle on which the fuel gage system 200 is mounted istraveling at a constant velocity on a level road, then the summation ofthe individual signals from load cells 202, 204 and 206 will give anaccurate indication of the weight of the fuel and fuel tank. If theweight of the empty fuel tank is known and previously stored in a memorydevice located in the processing unit 260, the weight of fuel in thetank can be determined by subtracting the empty tank weight from thissum of the load cell readings multiplied by an appropriate gage factorto translate the load cell signal sum into a weight. This result canthen be displayed on display 270 indicating to the vehicle operator theamount of fuel which remains in the tank.

[0088] If the vehicle on which the fuel tank system 200 is mountedbegins descending a steep hill, a summation of the signals from loadcells 202, 204 and 206 no longer accurately represents the weight of thefuel tank and fuel therein. As explained above, this is a result of thefact that the load cells are sensitive to forces along the vehicle yawaxis which now is different from the vertical or gravitational axis. Inaddition, unless the fuel tank is either full or empty, the forces onthe load cells will also be affected by the movement of fuel within thetank. When the vehicle is descending a hill, for example, the fuel willtend to move within the tank toward the front of the vehicle. Thesecombined effects create a unique set of signals from the three loadcells from which the angle of the fuel tank as well as the weight of thetank and fuel therein can be uniquely determined. In other words, forevery particular set of load cell readings there is only onecorresponding combination of vehicle pitch and roll angles and quantityof fuel in the tank. Therefore, if the load cell readings are known thequantity of fuel in the tank can be determined.

[0089] Since this concept is central to this invention and applieswhether load cells, angle gages and/or level gages are used, considerthe following illustration. It is assumed that all parts both above andbelow the fuel surface are connected so that both air and fuel can flowfreely from any part to any other part of the tank. If the tank at timeTi has a quantity of fuel Q1 and is tilted at a roll angle of R1 and apitch angle of P1, then the three load cells will measure loads L1, M1and N1 respectively. If the roll angle of the tank is now changed by asmall amount to R2 with the pitch angle and quantity of fuel remainingthe same, then the load cells will register a new set of loads L2, M2and N2 where each load reading will either increase or decreasedepending on the direction of the roll and the placement of the loadcells. The sum of the three load cell readings after correction for theroll and pitch angles, must still add up to the weight of the fuel inthe tank.

[0090] If the tank is empty it is easily proven from simple staticequations that there is a unique set of loads Li, Mi and Ni for everypitch and roll angle Pi and Ri. Alternately, if Li, Mi and Ni are knownand if the weight of the empty tank is known, the angles Pi and Ri canbe easily found. If a small quantity of fuel is now added to the tankand the angles held constant than all of the load cells will measure anincrease in load which will depend on the angles and the shape of thetank. Thus for a given set of angles, there is a unique relationshipbetween the three load cell readings and the quantity of fuel in thetank. If the fuel is held constant and the roll angle of the tank ischanged, the sum of the load cell readings, when corrected for theangles, must remain the same but the distribution of the loads willchange as the fuel moves within the tank. This distribution, however,follows a function determined by the shape of the tank. If the rollincreases to R2 and then increases to R3, and if L2 is greater than L1after correction for the angles then L3 must be greater than L2 aftercorrection for the angles. The same holds true for the M and N load cellreadings.

[0091] The distribution of the load cell readings L, M and N in fact canbe used to determine the angle of the tank and thus provide theinformation as to what the angle corrections need to be. This lattercalculation need not be made directly since the relationship between thefuel quantity and the individual load cell readings must be determinedfor all but the simplest cases by deriving an empirical relationshipfrom experiments. Most appropriately, the empirical relationship betweenthe three load cell readings, the pitch and roll angles and the fuelquantity is trained into a neural network

[0092] The same argument holds for changes in the pitch angles of thetank and it follows, therefore, that for every value of L, M and N thereis a unique quantity of fuel, pitch angle and roll angle for the tank.This argument fails if there is more than one distribution of fuel inthe tank for a given pitch or roll angle which would happen if the fueland air volumes are not connected. If, for example, a quantity of fuelor a quantity of air can become trapped in some part of the tank for aparticular sequence of motions but not for another sequence where bothsequences end at the same pitch and roll angles, then the problem wouldbe indeterminate using the methods so far described unless the motionsequence were recorded and taken into account in the calculations. Thisis not an insurmountable problem and will be discussed below.

[0093] A similar argument holds for the case where the pitch and rollangles are measured but only a single load cell is used to measure theload at one point or a single level gage is used to measure the level atone point in the tank, provided the level measured is neither empty norfull. This is a preferred implementation when an IMU is present on thevehicle for other purposes with the pitch and roll data available on avehicle bus. An even more refined measurement can result if the linearand angular accelerations and velocities are also used in thecalculation where appropriate. To this end, sensors and processors fordetecting and/or determining the linear and angular accelerations couldbe provided, to the extent the determination of the linear and angularaccelerations cannot be determined by devices already present on thevehicle.

[0094] For some simple tank geometries this relationship can beanalytically determined. As the complexity of the tank shape increases,it becomes more difficult to obtain an analytical relationship and itmust be empirically determined.

[0095] The empirical determination of the relationship between the trueweight of the vehicle tank and its contents can be determined for aparticular tank as follows. A test apparatus or rig is constructed whichsupports the gas tank from the three load cells, for one preferredimplementation, in a manner identical to which it is supported by thefloor-pan of the candidate vehicle. The supporting structure of the rig,however, is mounted on gimbaled frames which permit the tank to berotated about either of the roll or pitch axes of the tank or anycombination thereof. Stepping motors are then attached to the gimbaledframes to permit precise rotation of the tank about the aforementionedroll and pitch axes. Under computer control of the stepping motors, thetank to be tested is rotated to all positions representing allcombinations of pitch and roll angles where each rotation is performedin discrete steps of, for example, one degree. For each position of thetank, the computer samples the signals from each of the load cells andrecords the data along with the pitch and roll angles. The maximum pitchand roll angles used for this experiment are typically ±15 degrees.

[0096] To illustrate the operation of the experiment, the first readingof the three load cells would be taken when the roll and pitch anglesare at zero degrees and the tank is empty. The second reading would betaken when the pitch angle is one degree and the roll angle is zerodegrees and the third reading when the pitch angle is at two degrees andso on until a pitch angle of fifteen degrees had been achieved. Thisprocess would then be repeated for pitch angles starting at −1 degreeand decreasing until the pitch angle is −15 degrees. The next series ofreadings would be identical to the first series with the roll angle nowheld at one degree. The process would be repeated for roll angles up to15 degrees and then from −1 degree to −15 degrees. Since there are 31different pitch angles and 31 different roll angles a total of 961different sets of load cell readings will be taken and stored by thecomputer system.

[0097] The process now must be repeated for various quantities of fuelin the tank. If the full tank contains 20 gallons of fuel, therefore,and if increments of one gallon are chosen, the entire process ofcollecting 961 sets of data must be taken for each of the 21 quantitiesof fuel ranging from 0 to a full tank. In addition to the load cellreadings, it is also desirable to accurately measure the angle of thefuel tank through the use of angle gages in order to verify the steppingmotor positioning system. Thus, for each position and fuel quantitydiscussed above there will be two additional data representing the pitchand roll angles of the gas tank. This leads to a grand total of 100,905data elements.

[0098] From this data, a variety of different fuel gage designs based onthe use of load cell transducers can be made. The same process can alsobe done for designs using other types of transducers such as theconventional float system, the ultrasonic system, the rod-in-tubecapacitor system and the parallel plate capacitor system describedbelow.

[0099] Although a considerable quantity of data is obtained in the abovedescribed empirical system, this is not a complex task for a standardpersonal computer with appropriate data acquisition hardware andsoftware. The resulting data provides in tabular form the relationshipbetween the quantity of fuel in the tank and the readings from the threeload cells 202, 204 and 206. This data, or a subset of it, can beprogrammed directly as a look-up table into the computer algorithm. Thealgorithm would then take the three load cell readings and usinginterpolation formulas, determine the quantity of fuel in the tank.However, at the present time, the data can be used to train a neuralnetwork.

[0100] Naturally the particular quantity of data taken, the pitch androll angle steps and the fuel quantity steps are for illustrativepurposes only and an empirical relationship can be found using differentexperimental techniques.

[0101] If one or more equations are desired to represent the data thenthe next step in the process is to analyze the data to find amathematical expression which approximately represents the relationshipbetween the load cell readings and the fuel in the tank. It has beenfound, for example, that a simple fifth order polynomial is sufficientto accurately relate the load cell readings to the fuel tank weightwithin an accuracy equivalent to 0.1 gallons of fuel for the particulartank of simple geometry analyzed. Naturally, a more complex mathematicalfunction would give a more accurate representation and a less complexrelationship would give a less accurate representation. A fifth orderpolynomial requires the storage of approximately 200 coefficients.However, because of tank symmetry it has been found that approximatelyhalf of these coefficients are sufficiently close to zero that they canbe ignored. An alternate approach is to use a neural network which canbe trained to give the quantities of fuel based on the three load cellinputs.

[0102] In the above discussion, it has been shown that the referencemass used in the Grills et al. patent can be eliminated if theindividual load cell readings are analyzed independently rather thanusing their sum, as in the Grills patent, and an empirically determinedrelationship is used to relate the individual load cell readings to theweight of the tank. By substituting an algorithm for the physicalcomponents in the Grills patent, a significant system cost reductionresults. Although the system described above is quite appropriate foruse with land operated vehicles where the pitch and roll angles arelimited to 15 degrees, such a system may not work as well for aircraftwhich are subjected to substantially higher inertial forces and greaterpitch and roll angles.

[0103] A discussion of various load cell and other transducer designsappears below. All of the load cell designs make use of a strain gage asthe basic load measuring element. An example of a four element metalfoil strain gage is shown in FIG. 3. In this example, the gage is aboutone centimeter on each side thus the entire assembly of the fourelements occupies about one square centimeter of area of the beam onwhich it is mounted. In this case, the assembly is mounted so thatelements 301 and 303 are aligned with the conductive pattern parallelwith the axis of the beam, and elements 302 and 304 are aligned withtheir conductive pattern transverse to the beam. The elements are wiredas shown with the two free ends 315 and 316 left unconnected so that anexternal resistor can be used to provide the final balance to the bridgecircuit. The elements thus form a Wheatstone bridge which when balancedresults in a zero current in the indicator circuit as is well known tothose skilled in the art.

[0104] When the beam is bent so that the surface on which the straingage is mounted experiences tensile strain, elements 301 and 303 arestretched which increases their resistance while elements 302 and 304are compressed by virtue of the lateral contraction of the beam due tothe Poisson's ratio effect. Due to the manner in which the elements arewired, all of the above strains result in an increase in the currentthrough the indicator circuit, not shown, thus maximizing the indicatorcurrent and the sensitivity of the measurement. If the temperature ofthe beam and strain element changes and if there is a mismatch in thethermal coefficient of expansion between the material of the strain gageand the beam material, all of the gage elements will experience the sameresistance change and thus it will not affect the current in theindicator circuit. Thus, this system automatically adjusts for changesin temperature.

[0105] The metal material which forms the strain gage is photo etchedfrom thin foil and bonded onto a plastic substrate 310. Substrate 310 isthen bonded onto the beam using appropriate adhesives as is wellunderstood by those skilled in the strain gage art. A similar geometrycan be used for SAW strain gages.

[0106] The tank weighing system illustrated in FIG. 2 is highly accuratewith a root mean square error of typically less than 0.1 gallons out ofa 20 gallon tank. This corresponds to a travel distance of approximately2 to 3 miles which is about 3 to 5 kilometers. For many cases accuracyof this order is not necessary and a simpler system such as shown inFIG. 4 can be used. In this case, the load cell signals are merelysummed as in the case of the Grills patent but without the use of areference mass. In this case no attempt is made to compensate for thepitch or roll of the vehicle. The maximum grade on a highway in theUnited States is about 15 degrees and any grade above 5 degrees isunusual. When the vehicle is on a 15 degree grade the weighing system ofFIG. 4 will be in error by about 3.4% and for a 5 degree grade the erroris about 0.4%. As will be discussed below, the variation in specificgravity of fuel is about 5%. Fuel energy content and thus usage is moreclosely related to the fuel weight than to volume and thus the mere useof volume instead of weight as the measure of the quantity of fuel in avehicle by itself results in an error in the distance that a vehicle cantravel of up to 5%.

[0107] In FIG. 4, the load cells 202, 204 and 206 are electricallyconnected to a summing circuit, not shown, which is part of theelectronic package 250. The summed signal is then fed into analog todigital converter (ADC) 258 and from there to the processing unit 260.

[0108] The accuracy of the system shown in FIG. 4 can be improvedthrough the use of a roll sensor 502 and a pitch sensor 504 as shown inFIG. 5. The addition of these two sensors regains the accuracy lost ingoing from the system of FIG. 2 to the system of FIG. 4. The roll andpitch sensors are shown mounted to the fuel tank in FIG. 5 so that theyaccurately measure the angles of the fuel tank. For most applications,it would be sufficient to mount these sensors within the electronicpackage 250 as described in more detail below. In FIG. 5, the roll andpitch sensors 502 and 504 are electrically connected to ADCs 552 and 554respectively which are in turn connected to processing unit 560.

[0109] The design of the system shown in FIG. 2 can also be simplifiedif it is assumed that the effects of roll can be ignored or averaged outover time and that only corrections for pitch need be made. Such asystem is illustrated in FIG. 6 where only two load cells 202 and 608are used. These load cells are electrically connected to ADCs 252 and658 respectively in a similar manner as described above.

[0110] Once again all of the accuracy lost in going from the FIG. 2design to the FIG. 6 design can be regained through the addition ofpitch and roll sensors 502 and 504, an IMU, or for that matter with theaddition of just roll sensor 504, as illustrated in FIG. 7 (i.e., sothat a minimum of three parameters are used-the pitch angle, the rollangle and the load at the single load cell). In a similar manner as inthe FIG. 2 case, a rig is required to test a particular tank anddetermine the proper empirical relationship which relates the anglemeasurements from roll and pitch gages 502 and 504 and the loadmeasurements from load cells 608 and 202 to the volume of fuel in thetank.

[0111] In all of the cases described above including the case describedin the Grills et al. patent, provision must be made to arrest thelateral and longitudinal vibrations which will occur as a vehicletravels down the road. This is usually accomplished by placing deviceswhich impose lateral and longitudinal forces onto the tank to counteractsimilar forces caused by the motion of the vehicle and the inertia ofthe tank. Care must be taken in the design of these devices so that theydo not impose forces onto the tank in the vertical or yaw directionotherwise errors will be introduced into the weight measurements. As aminimum, these devices add complexity and thus cost to the system.

[0112] This problem of constraining the tank so that it can only move inthe vertical direction is accomplished by the system shown in FIG. 8which is the preferred implementation of this invention using load celltransducers. In the embodiment shown in FIG. 8, a single load cell 202is used to obtain a weight measurement of a portion of the tank. Asignificant portion of the tank weight is now supported by a hingesystem 890 which effectively resists any tendency of the tank to move ineither the lateral or longitudinal directions thus eliminating the needfor special devices to oppose these motions.

[0113] Since there is only a single load cell 202 which only supports aportion of the weight of the tank, significant errors would occur ifthis weight alone were used to estimate the weight of the tank.Nevertheless, as before there is a unique relationship between thevolume of fuel in the tank and the weight as measured by load cell 202plus the roll and pitch angles as measured by the roll and pitch sensor880, or an IMU. For a particular load cell signal and a particular rollangle and pitch angle, there is only one corresponding volume of fueland thus the system is determined from these three measurements. Onceagain the rig described for the FIG. 2 system could be employed todetermine the proper mathematical relationship to relate these threemeasured values to the fuel volume and once again the accuracy whichresulted from performing such a procedure on a particular fuel tankdesign is a root mean square error of about 0.1 gallons using a fifthorder polynomial approximation or even less using a look-up table.

[0114] The system of FIG. 8 is thus the simplest and least expensivesystem and also about the most accurate system of those described thusfar in this specification. The pitch and roll sensor is now a singledevice providing both measurements and is mounted within the electronicpackage 850, again an IMU can be used for even greater accuracy. Oneparticular pitch and roll sensor which has been successfully used inthis application is manufactured by Fredricks of Huntingdon, Pa. and isknown as the Fredricks tilt sensor. It is an inexpensive device whichuses the variation in resistance caused by tilting the device of aresistance element using an electrolyte. This resistance also varieswith temperature which can be compensated for but requires additionalADCs. When this is done, the roll and pitch angles can be accuratelymeasured to within about 0.1 degree regardless of the temperature. Therequirement to compensate for temperature changes, however, requiresthat outputs be taken across both sides of the two angle measuringelements necessitating the use of four ADCs rather than two. Low costmicroprocessors are now available with up to eight ADCs integral withthe processor so that the added requirement for the resistancemeasurement can be accommodated at little additional expense. In FIG. 8,therefore, the pitch and roll angle sensor 880 is electrically connectedto ADCs 881, 882, 883 and 884 and from there to processing unit 260 asdescribed above.

[0115] In many vehicles, the fuel tank is exposed to the under side ofthe vehicle and therefore to the mud, ice and snow which is thrown up asthe vehicle travels down the roadway. If the tank is exposed, some ofthis mud can collect on the tank and particularly on top of the tank.This mud will necessarily add to the tank weight and introduce an errorin the weighing system. The magnitude of this error will depend on thegeometry of a particular tank design. Nevertheless, in many applicationsthis error could be significant and therefore the tank should beprotected from such an event. This can be accomplished as shown in FIG.9 through the addition of a skirt 972 which is below the tank and whichseals it preventing mud, ice or snow from getting into contact with thetank. If the addition of such a skirt is not practical, then a systemusing one or more fuel level gages or measuring devices as describedbelow is preferred.

[0116] As discussed above, the specific gravity of automobile gasolinevaries by about ±4% depending on the amount of alcohol added, the gradeand the weather related additives. The energy content of gasoline ismore closely related to its weight than to its volume and therefore theweight of fuel in a tank is a better measure of its contents. Fuelweight is commonly used in the aircraft industry for this reason but theautomobile driving public is more accustomed to thinking of fuel byvolume measurements such as gallons or liters. To correct for thisperceived error, a device can be added to any of the above systems tomeasure the specific gravity of the fuel and then make an appropriateadjustment in the reported volume of fuel in the tank.

[0117] Such a device is shown generally as 1010 in FIG. 10 and consistsof a mass 1012 having a known specific gravity and a cantilevered beamload cell 1014. By measuring the weight of mass 1012 when it issubmerged in fuel, a calculation of the specific gravity of the fuel canbe made. Naturally, the tank must have sufficient fuel to entirely coverthe mass 1012 and the load cell 1014 in order to get an accuratereading. Therefore, the processing unit 260 will utilize informationfrom the specific gravity measuring device 1010 when the weighing systemconfirms that the fuel tank has sufficient fuel to submerge mass 1012.

[0118] A cantilevered beam load cell design using a half bridge straingage system is shown in FIG. 11. The remainder of the Wheatstone bridgesystem is provided by fixed resistors mounted within the electronicpackage which is not shown in this drawing. The half bridge system isfrequently used for economic reasons and where some sacrifice inaccuracy is permissible. The strain gage 1110 includes strain measuringelements 1112 and 1114. The longitudinal element 1112 measures thetensile strain in the beam when it is loaded by the fuel tank, notshown, which is attached to end 1122 of bolt 1120. The load cell ismounted to the vehicle using bolt 1130. Temperature compensation isachieved in this system since the resistance change in strain elements1112 and 1114 will vary the same amount with temperature and thus thevoltage across the portions of the half bridge will remain the same.

[0119]FIG. 11A illustrates how the load cell of FIG. 11 can be mountedto the vehicle floor-pan 18 and the fuel tank 14 by means of bolts 1130and 1120 respectively.

[0120] One problem with using a cantilevered load cell is that itimparts a torque to the member on which it is mounted. One preferredmounting member on an automobile is the floor-pan which will supportsignificant vertical loads but is poor at resisting torques sincefloor-pans are typically about 1 mm (0.04 inches) thick. This problemcan be overcome through the use of a simply supported load cell designas shown in FIG. 12.

[0121] In FIG. 12, a full bridge strain gage system 1210 is used withall four elements mounted on the top of the beam 1205. Elements 1212 aremounted parallel to the beam and elements 1214 are mounted perpendicularto it. Since the maximum strain is in the middle of the beam, straingage 1210 is mounted close to that location. The load cell, showngenerally as 1200, is supported by the floor-pan, not shown, at supports1230 which are formed by bending the beam 1205 downward at its ends.Plastic fasteners 1220 fit through holes 1222 in the beam and serve tohold the load cell 1200 to the floor-pan without putting significantforces on the load cell. Holes are provided in the floor-pan for bolt1240 and for fasteners 1220. Bolt 1240 is attached to the load cellthrough hole 1250 of the beam 1205 which serves to transfer the forcefrom the fuel tank to the load cell.

[0122] The electronics package is potted within hole 1262 using urethaneor silicone potting compound 1244 and includes a pitch and roll dualangle sensor or IMU 1270, a microprocessor with integral ADCs 1280 and aflex circuit 1275. The flex circuit terminates at an electricalconnector 1290 for connection to other vehicle electronics. The beam isslightly tapered at location 1232 so that the strain is constant in thestrain gage. If an IMU is used, the ADCs relative to the IMU could bepart of the IMU and if SAW strain gages are used, the ADCs may be partof the general interrogator.

[0123]FIG. 12A illustrates how the load cell of FIG. 12 can be mountedto the vehicle floor-pan 18 and the fuel tank 14 by means of plasticfasteners 1220 and bolt 1240 respectively.

[0124] Although thus far only beam type load cells have been described,other geometries can also be used. One such geometry is a tubular typeload cell. Such a tubular load cell as shown generally at 1300 in FIG.13 can be placed either above or below the floor-pan. It consists of aplurality of strain sensing elements 1310 for measuring tensile andcompressive strains in the tube as well as other elements, not shown,which are placed perpendicular to the elements 1310 to provide fortemperature compensation. Temperature compensation is achieved in thismanner, as is well known to those skilled in the art of the use ofstrain gages in conjunction with a Wheatstone bridge circuit, sincetemperature changes will affect each of the strain gage elementsidentically and the total effect thus cancels out in the circuit. Thesame bolt 1340 can be used in this case for mounting the load cell tothe floor-pan and for attaching the fuel tank to the load cell.

[0125]FIG. 13A illustrates how the load cell of FIG. 13 can be mountedto the vehicle floor-pan 18 and the fuel tank 14 by means of bolt 1340.

[0126] Another alternate load cell design shown generally in FIG. 14 as1400 makes use of a torsion bar 1410 and appropriately placed torsionalstrain sensing elements 1420. A torque is imparted to the bar 1410 bymeans of lever 1430 and bolt 1440 which attaches to the fuel tank notshown. Bolts 1450 attach the mounting blocks 1460 to the vehiclefloor-pan. FIG. 14A illustrates how the load cell of FIG. 14 can bemounted to the vehicle floor-pan 18 and the fuel tank 14 by means ofbolts 1450 and 1460 respectively.

[0127] A torsional system is disclosed in the Kitagawa et al. patentreferenced above, however, a very complicated electronic system notinvolving strain gage elements is used to determine the motion of thelever arm. Torsional systems in general suffer from the same problems ascantilevered systems in that they impart a torque to the mountingsurface. If that surface is the floor-pan, undesirable deformationscould take place in the floor-pan and the direction of the load cellsensitive axis cannot be guaranteed.

[0128] Until recently, most automobile fuel tanks were made from metaland load cells could be most readily attached to the fuel tank usingbolts or metal fasteners. With the advent of plastic fuel tanks, otherattachment means are preferred. One such method is shown in FIG. 15where the fuel tank support is designed into the tank. This design showngenerally as 1500 in FIG. 15 permits the load cell 1520 to be placedapproximately on the center of gravity of the fuel tank when it is fullof fuel. When the gas tank 1510 is formed, a hole 1530 is providedthrough the tank. An extended tubular load cell 1520 passes through thishole and connects to plate 1540 at the bottom of the tank by means of anut 1550 or other appropriate fastener. Plate 1540 is of sufficient sizeto support the entire tank. Tabs 1580, located at appropriate positionsaround the periphery of the tank, snap into corresponding cooperatingreceptors, not shown, placed on the vehicle and serve to give lateraland longitudinal support to the tank to minimize vibrations withoutloading the tank in the vertical direction.

[0129] The load cells illustrated above are typically of the foil straingage type. Other types of strain gages exist which would work equallywhich include wire strain gages and strain gages made from silicon.Silicon strain gages have the advantage of having a much larger gagefactor and the disadvantage of greater temperature effects. Other straingage materials and load cell designs are of course possible to beincorporated within the teachings of this invention and those using SAWtechnology in particular.

[0130] When pitch and roll sensors have been used herein, it was assumedthat they would be dedicated devices to this tank gaging system. Othersystems which are either already on vehicles or are planned for futureintroduction also have need for pitch and roll information and mayrequire devices which are either more accurate or have a faster responsethan the devices required for this application. These other anglesensors may be usable by the systems disclosed herein therebyeliminating the need for dedicated angle gages and further reducing thecost of the system. In particular, an IMU that will probably be onfuture vehicles fits this description.

[0131] It is contemplated that the algorithms used for relating thevarious measured parameters to the volume of fuel in the tank will beindependent of the particular vehicle on which the system is used aslong as the fuel tank shape is the same. Fuel tanks even of the samedesign will vary in weight due to manufacturing tolerances andtherefore, in some cases, it is desirable to weigh the tank after it ismounted onto the vehicle and just before it is filled with fuel. Thiscan be programmed into the processing unit so that when it is firstactivated it will store the tank weight for later calculations.

[0132] Generally, the Wheatstone bridge is balanced with no load on thestrain elements. An alternate method is to balance the bridge with theweight of the empty tank loading the load cell and therefore strainingthe strain gage elements. This results in the maximum accuracy andremoves the requirement to subtract out the weight of the empty tank inthe weight calculations. In a similar vein, the entire system can bedesigned to operate using dynamic measurements rather than staticmeasurements, or in addition to static measurements, thus eliminatingthe effect of residual stresses.

[0133] The invention disclosed herein has been illustrated above inconnection with embodiments using load cell transducers. Other types oftransducers can also be used in conjunction with a derived algorithm orrelationship providing certain advantages and disadvantages overweighing systems. A key problem with weighing systems is that the tankmust be free to move in the vertical direction. Current gas tank systemsare frequently strapped against the underside of the automobile, and infact for modern plastic tanks this represents an important part of thegas tank supporting system. As the temperature changes within the gastank, significant pressures can build up and cause the tank to expand ifit is not restrained. A system using weighing transducers, therefore,would also need to provide for additional structure to prevent thisexpansion. This additional structure naturally adds to the cost of thesystem and, at least when plastic tanks are used, favors the use ofnon-weighing transducers such as the conventional float system.

[0134] Such a system is illustrated in FIG. 16 which is a perspectiveview with portions cut away of an automobile fuel tank 900 with aconventional float 910, shown schematically, and variable resistormechanism 920 used in combination with a pitch and roll angle measuringtransducer 880, analog-to-digital converters 881, 882, 883, 884 and 952and associated processor 260. The addition of the angle measuringtransducer and the processor and appropriate algorithm relating thetransducer outputs to the fuel level (which may be replaced by a trainedneural network), significantly increases the accuracy of theconventional float level measuring device. Nevertheless, the variableresistor does not have the resolution of the load cell transducersdescribed above and the float, by virtue of its height, is subject inconventional designs to topping and bottoming out making it impossibleto achieve accurate measurements when the tank is almost full or almostempty. Thus, significant improvements are obtained with this system butsignificant limitations relating to the float system remain. The mainadvantage of this system and the ones described below is that the tank(whether plastic or metal) does not need to be modified.

[0135] Before continuing with a description of other preferredembodiments of the fuel gage of this invention, a summary of the abovedevelopments is in order. The initial system which was considered wassomewhat similar to the one disclosed in the Grills et al. patent. Thissystem was judged overly complicated for use in automobiles and it wasfound that similar accuracy could be achieved by eliminating thereference mass and load cell and by treating the three supporting loadcells independently thereby extracting more information from each loadcell at the expense of a more complicated electronic system involving amicroprocessor and algorithm. Nevertheless this was an important step,going from a system which would theoretically give an exact answer toone which involved less hardware but which would theoretically only givean approximate solution, albeit one which could be made as accurate asdesired. Once it was decided that an approximate method was feasible,the next step was to further simplify the hardware by eliminating twomore of the load cells and substitute a far less expensive dual anglesensor or better to use an IMU that already existed on the vehicle. Onceagain it was found that the approximate solution could be made asaccurate as desired using the single load cell output plus the anglesensor outputs as data.

[0136] The next step was to realize that once the exact solution hadbeen abandoned, many other transducer types could be used as long asthey give a continuous reading of some measure of the fuel in the tankas the tank goes from full to empty. The natural choice was theconventional float system which, when coupled with the dual angle gage,or IMU, would provide a significant improvement over the current floatsystem alone. The float system suffers from its inability to measure thefuel level when the tank is either near empty or near full since,because of its thickness in the vertical direction, it will necessarilytop out or bottom out.

[0137] The need to consider other transducer types in place of weighingstems from the peculiarities of modem fuel tanks and their supportingsystems. There is a movement toward plastic tanks not only because oftheir lighter weight and lower manufacturing costs but also because theyare less likely to rupture in rear and side impacts, that is they arealso safer. Also, fuel tanks are frequently exposed to the environmentunderneath the vehicle where they can accumulate mud, ice and snow whichaffects the weight of the tank and thus the accuracy of the system.Finally, automobile operators are accustomed to thinking of fuel byvolume while weighing systems naturally measure weight. This naturallyleads to additional errors unless the density of the fuel is alsomeasured which adds cost and complexity to the system. For the abovereasons, the progression was to take what was learned about approximatemethods and apply it to systems using other fuel level measuring systemsas discussed below.

[0138] An alternate method to the use of a float for determining thelevel of fuel in a gas tank uses the fact that the dielectric constantof gasoline is higher than air. Thus, if the space between two plates ofa capacitor is progressively filled as the level of gas in the tankrises, the capacitance increases. One method of implementing this isillustrated in FIG. 17 which is a perspective view with portions cutaway of an automobile fuel tank 1000 with a rod-in-tube capacitive fuellevel measuring device 1010 used in combination with pitch and rollangle measuring transducers or IMU 880 as described above in FIG. 16.The dielectric constant of gasoline is about two and the capacitance fora typical rod and tube design goes from about 60 picofarads for an emptytank to 120 picofarads for a full tank. Capacitances of this magnitudecan be measured using technologies familiar to those skilled in the artbut generally require that the measuring circuitry 1050 be adjacent tothe device since the capacitance between the wires would otherwise besignificant. All of the electronics including the ADCs, angle gage andprocessor are thus encapsulated into a single package 1050 and attachedto the tube 1032.

[0139] The capacitor is formed by the rod 1031 and tube 1032 of FIG. 17Awith the fuel partially filling the space in between. In someapplications the tube 1032 is actually formed from two tubes 1032 a and1032 b which are electrically insulated form each other by spacer 1004.Tube 1032 a is located at the bottom of the tank where it is likely tobe completely filled when the tank is filled. This portion is used todetermine the dielectric constant of the gasoline and the combination ofthe two tubes 1032 a and 1032 b are used to determine the level of fuel.The processor remembers the dielectric constant of the fuel which wasmeasured when the tank was filled to a point that tube 1032 a was knownto be full of gasoline. That dielectric constant is then used as thetank level falls below the interface 1004 between tube 1032 a and tube1032 b. Although the dielectric constant of most constituents ofgasoline is about 2, the addition of alcohol or other additives togasoline can have an effect on the dielectric constant. One or moreopenings 1005 are provided in the base of the tube 1032A in order toprovide easy access for the fuel into and out of the gage.

[0140] The system shown in FIG. 17 thus has all of the advantages of thefloat system of FIG. 16 with the additional advantages of permittingmeasurement of the fuel level from full to empty and with significantlygreater resolution resulting from the no moving part capacitancemeasurement compared to the low resolution sliding contact rheostat ofthe float system.

[0141] An alternate method of using capacitance to measure the fuel inthe tank is shown in FIG. 18 which is a perspective view with portionscut away of an automobile fuel tank 1100 with a parallel platecapacitive fuel level measuring device, where the plates are integralwith the top and bottom of the fuel tank. This system can also be usedin combination with pitch and roll angle measuring transducers or IMU880 and associated electronic circuitry as in the preceding twoexamples. In this design, the tank top 1110 and bottom 1120 arepartially metalized so that they form the two plates of an approximatelyparallel plate capacitor. If the tank is symmetrical with a constantdistance between the top and bottom, the capacitance will not change asthe angle of the vehicle changes and the angle gages would not berequired. All real tanks, however, have significant asymmetriesrequiring the use of the angle gages or IMU 880 as above.

[0142] The system of FIG. 18 has one additional error source,illustrated schematically by the circuit diagram shown in FIG. 18A,which prevents its use in some vehicles. The bottom plate 1120 will alsohave a capacitance to the earth, shown as Cte, the earth will have acapacitance to the floor-pan of the automobile, shown as Cfe, and theautomobile floor-pan will have a capacitance to the tank top plate 1110,shown as Ctf. These three capacitances act in series to shunt thecapacitance between the tank plates 1110 and 1120 with a totalcapacitance of (Cte*Cfe*Ctf)/(Cte*Cfe+Cte*Ctf+Cfe*Ctf). This would notbe a problem except that the capacitances to the earth will varydepending on vehicle ground clearance and the constituents of the earthbelow the vehicle. In some cases it is possible to measure one of thecapacitances to the earth and compensate for this effect, in others theeffect is too large and another fuel gage design is required.

[0143] An alternate fuel level measuring system is shown in FIG. 19 anduses a transducer 1220 which produces waves which reflect off of thefuel/air surface 1210 and are received by the same transducer 1220 or,alternately by another receiver. The preferred waves are ultrasonic at apreferred frequency above 100 KHz, although an infrared laser system canalso be designed to accomplish the same task. Although the system shownin FIG. 19 uses only a single transmitting and receiving transducer,multiple such transmitters can be used in different parts of the tank.This is a particularly advantageous system when the tank has a complexshape such as those now being developed for various automobile models.

[0144] As efforts are intensifying to make use of all available spacewithin the automobile exterior envelope, fuel tanks are being designedand built with very complex shapes. The use of blow molded plastic tankshas made it easier to construct such complex shapes. In some cases, itis possible to place an additional float system within such a tank butonly with great difficulty. The placement of multiple ultrasonictransducers, on the other hand, is relatively easy. If two suchtransducers are used than one of the angle gages can be eliminated andif three such transducers are used then neither the pitch or roll anglegages are required (i.e., a minimum of three parameters must be known toaccurately determine the volume of fuel in the tank-the three parametersbeing selected from the group consisting of the first, second and thirdtransducers, the pitch angle gage and the roll angle gage). Alternately,with some loss of accuracy, two transducers will still give increasedaccuracy over current float based systems.

[0145] In the embodiment shown in FIG. 19A, ultrasonic transducers 1920and 1921, both of which both send and receive ultrasonic waves, areplaced at different points on the bottom of the fuel tank 1200.Ultrasonic waves from the transducer are reflected off of the fuelsurface 1210 thus giving a measurement of the height of fuel above thetransducers 1920, 1922. Outputs from these transducers 1920, 1922 arefed into ADCs 1152 and 1154 and combined with outputs from the pitch androll angle sensors or IMU, if present, are processed by processing unit260 to output a signal representative of the volume of fuel in the tank.Once again, processor 260 uses a derived relationship which may be alookup table, one or more mathematical formulae, or a patternrecognition system comprising a neural network, fuzzy logic or othersuch system.

[0146] So far, the discussion using ultrasonic transducers has beenlimited to the measurement of liquid level at a particular place in thefuel tank. The combination of ultrasonic transducers and neural networkscan also be used in a much more powerful manner. When an ultrasonictransducer sends waves through the liquid fuel, reflections occur fromnot only the nearest surface but also from all other surfaces whichinteract with the waves. Each wavelet on the surface of the fluidpotentially can reflect waves back toward the transducer givinginformation as to the location of the surface. If the transducer is ofthe type which transmits over a wide angle, then reflections will bereceived from a significant portion of the liquid surface. One suchtransducer, for example, operates at 40 kilohertz transmits with a 3 dbrolloff at about 60 degrees from the transmit axis of the device. Whenthis transducer is placed at the bottom of the fuel tank when thevehicle and fuel is at rest, the primary reflection will occur from thenearest surface and three such transducers can accurately measure thefuel level at all three positions. From these three measurements, inconjunction with a neural network, the quantity of fuel in the tank canbe readily determined. If the fuel is in motion, sloshing around withinthe tank, the problem is not as simple. These surface waves, on theother hand, now reflect back toward the transducer and provideinformation as to where the surface is everywhere within the tank.

[0147] When multiple reflections occur, they are spaced in timeaccording to the distance from the reflecting object or surface wave andthe transducer. Thus, if for example, the transducer sends out fourcycles of ultrasound, the transmitted cycles will reflect off of varioussurfaces, or wavelets, with the reflections spaced in time. That is, thereceiver will receive a return pulse which is many times longer than thetransmitted pulse and which contains information as to the shape of thesurface. If several such transducers are used and the received signalsare used to train a neural network, the resulting algorithm created bythe neural network program will accurately represent the relationshipbetween the reflected wave pattern and the quantity of fuel in the tank.

[0148] The process therefore is as follows. For a particular tank andvehicle, a known amount of fuel is placed into the tank and reflectedwave patterns are collected from the vehicle under various conditionsfrom at rest to driving over a variety of road surfaces, curves, hillsetc. Then the quantity of fuel is changed and the process repeated.After data is collected from the entire range of driving situations,including at rest at various angles, and fuel quantity, the data is fedinto a neural network program which derives an algorithm whichaccurately relates the quantity of fuel to the echo patterns. Theresulting algorithm is then made apart of a system for vehicleinstallation thereby providing the quantity of fuel from the echopatterns of the transducers as the vehicle is at rest or being operated.Modern plastic fuel tanks have a somewhat indeterminate shape in thatthe internal volume depends, among other things, on the force applied tothe tank by the mounting straps when the tank is assembled to thevehicle. The system described here can also be used to determine thetank volume before fuel is introduced into the tank by analyzing thereturn echoes from the tank surfaces. Once again, the neural networkwould need first to be trained to do this function by taking data oninstallations with varying amounts of mounting force. After that, thenetwork can determine the fuel capacity of the tank and thereby know thequantity of fuel in the tank based on an analysis of the return echoes.

[0149] One important feature of neural networks is that they can betrained on data from diverse sources. If, for example, information canbe provided as to the rate of fuel consumption such as provided byknowing the RPM of the vehicle engine, then, it can be also used by theneural network in the process of determining the amount of fuel in thetank. Such information can be quite important if coupled withinformation as to the last estimate made while the vehicle was at rest.Thus the history of the fuel measurements can also be used by the neuralnetwork to further improve the current estimate of fuel quantity.

[0150] This system can also solve the problem of occluded volumes. Aslong as the situations are included in the data on which the system istrained, it can be recognized later and thereby provide the correct fuelvolume based on the echo patterns.

[0151] Naturally, other fuel gages using a capacitor as the measuringtransducer can now be designed by those skilled in the art and thereforethis invention is not limited to those specific designs illustrated anddescribed above. In addition, other level measuring transducers can alsobe used in conjunction with angle gages, or an IMU, and an algorithmdeveloped by those skilled in the art and therefore this invention isnot limited to those specific methods illustrated and described above.In particular, although not illustrated herein, level sensors based onultrasonic or electromagnetic principles could be used along with anglegages and an algorithm according to the teachings of this invention.

[0152] Generally, when it is desirable to digitize different analogsignals, different ADCs are used. An alternate method is to use fewerADCs and a method of either multiplexing the signals for laterseparation or to switch the ADCs from one analog input to another.

[0153] A general SAW temperature and pressure gage which can be wirelessand powerless is shown generally at 70 located in a sidewall 73 of afluid container or reservoir 74 in FIG. 20. A pressure sensor 71 islocated on the inside of the container or reservoir 74, where itmeasures deflection of the reservoir wall, or of a specially constructeddiaphragm inserted into the sidewall 73 of the reservoir 74, and thefluid temperature sensor 72 on the outside. The temperature measuringSAW 70 can be covered with an insulating material to avoid influencefrom the ambient temperature outside of the container 74.

[0154] (this is the parent application described above!!!) Disclosedabove are multiple means for determining the amount of fuel in a fueltank. Using the SAW pressure devices of this invention, multiplepressure sensors can be placed at appropriate locations within a fueltank to measure the fluid pressure and thereby determine the quantity offuel remaining in the tank. This is illustrated in FIG. 21. In thisexample, four SAW pressure transducers 100 are placed on the bottom ofthe fuel tank and one SAW pressure transducer 101 is placed at the topof the fuel tank to eliminate the effects of vapor pressure within tank.Using neural networks, or other pattern recognition techniques, thequantity of fuel in the tank can be accurately determined from pressurereadings from transducers 100, 101 in a manner similar that describedabove.

[0155] The SAW measuring system illustrated in FIG. 21A combinestemperature and pressure measurements in a single unit using parallelpaths 102 and 103 in the same manner as described above.

[0156] Finally, the Grills et al. and Kitagawa et al. patents discussthe problems of fuel sloshing in the tank and disclose various averagingtimes and techniques for eliminating sloshing and other transienteffects. Similar methods are used in the invention disclosed herein forsimilar purposes and are included in the scope of this invention.

[0157] The invention described above is, of course, susceptible to manyvariations, modifications and changes, all of which are within the skillof the art. It should be understood that all such variations,modifications and changes are within the spirit and scope of theinvention and of the appended claims. Similarly, it will be understoodthat applicant intends to cover and claim all changes, modifications andvariations of the examples of the preferred embodiments of the inventionherein disclosed for the purpose of illustration which do not constitutedepartures from the spirit and scope of the present invention asclaimed.

[0158] What is claimed is:

We claim:
 1. A method for use in measuring the volume of fuel in a fueltank in a vehicle subject to varying external forces caused by movementand roll and pitch angles of the vehicle, comprising the steps of:mounting a fuel tank to the vehicle so that it is movable along the yawor vertical axis of the vehicle; providing at least one analog signal inproportion respectively to the load on at least one tank load cell, eachof the cells being placed between a portion of the fuel tank and aportion of a reference surface of the vehicle, and the cells beingsensitive along an axis substantially normal to the reference surfaceand generally parallel to the yaw axis of the vehicle; providing signalsproportionally representing the pitch or roll angles of said vehicle;and converting the at least one analog cell signal and the pitch or rollangle signals into output information representative of the volume ofthe liquid in the fuel tank by converting the at least one analog cellsignal to a digital signal and inputting the digital signal and thepitch and roll signals into a processor having an algorithm, thealgorithm using (i) the inputted at least one analog cell signal and thepitch or roll signals independently (ii) with a derived relationshipbetween the signals and the fuel volume to output the fuel volumeinformation.
 2. An apparatus for use in measuring the volume of a liquidin a fuel tank in a vehicle subject to varying external forces caused bymovement or changes in the roll and pitch angles of the vehicle,comprising: a fuel tank mounted to the vehicle and subject to forcesalong the yaw axis of the vehicle; at least one tank load cell forproviding an output proportionally representing the load on said loadcell, said load cell being mounted between a portion of said fuel tankand a portion of a reference surface of the vehicle, said load cellsbeing sensitive along an axis that is substantially normal to saidmounting surface and generally parallel to the yaw axis of the vehicle;and, computational means for performing a derived relationship betweensaid load cell output and the volume of fuel in said tank so as toconvert said output signal from said load cell into output informationrepresentative of the volume of the fuel in said tank.
 3. An apparatusfor use in measuring the volume of a liquid in a fuel tank in a vehiclesubject to varying external forces caused by movement or changes in theroll and pitch angles of the vehicle, without the use of a referencestandard of known weight, comprising: a fuel tank mounted to the vehicleand subject to forces along the yaw axis of the vehicle; weighing meansfor weighing said fuel tank and providing an output signalrepresentative of the weight of said tank; means for retaining datarepresentative of the known tank empty weight; and, computational meansto perform a derived relationship between the output of said weighingmeans and the volume of fuel in said tank so as to convert the output ofsaid weighing means into output information representative of the volumeof the fuel in said tank.
 4. An apparatus for use in measuring thevolume of a liquid in a fuel tank in a vehicle subject to varyingexternal forces caused by movement or changes in the roll and pitchangles of the vehicle, comprising: a fuel tank mounted to the vehicleand subject to forces along the yaw axis of the vehicle; level measuringmeans for measuring the level of fuel in said tank and providing anoutput signal representative thereof; angle measuring means formeasuring at least one of the pitch or roll angle of the vehicle andproviding an output signal representative thereof; and computationalmeans to convert said output signals from said level measuring means andsaid angle measuring means into output information representative of thevolume of the fuel in said tank.
 5. The apparatus of claim 4, whereinsaid level measuring means comprises a float and variable resistor. 6.The apparatus of claim 4, wherein said level measuring means comprises avariable capacitance capacitor.
 7. The apparatus of claim 4, whereinsaid level measuring means comprises an ultrasonic transmitter andreceiver for directing ultrasonic waves toward a surface of the fuel insaid tank and receiving ultrasonic waves reflected therefrom.
 8. Theapparatus of claim 4, wherein said level measuring means anelectromagnetic transmitter and receiver for directing electromagneticwaves toward a surface of the fuel in said tank and receiving ultrasonicwaves reflected therefrom.
 9. The apparatus of claim 4, wherein saidcomputational means comprises a processor embodying a mathematicalalgorithm.
 10. The apparatus of claim 4, wherein said computationalmeans comprises a processor embodying a neural network.
 11. An apparatusfor use in measuring a level of a liquid in a fuel tank in a vehiclecomprising: a fuel tank mounted to the vehicle; capacitor means formeasuring a level of fuel in said tank and providing having an outputsignal representative thereof, and computational means for convertingsaid output signal from said capacitor means into output informationrepresentative of a level of the fuel in said tank.
 12. The apparatus ofclaim 11, wherein said capacitor means comprises a tube.
 13. Theapparatus of claim 11, wherein said capacitor means comprises a plate.14. The apparatus of claim 11, wherein said capacitor means comprises apair of horizontal conductive members extending substantially along thetop and bottom of said tank.
 15. An apparatus for use in measuring alevel of a liquid in a fuel tank in a vehicle comprising: a fuel tankmounted to the vehicle; ultrasonic means for measuring a level of fuelin said tank and providing an output signal representative thereof; andcomputational means for convert said output signal from said ultrasonicmeans into output information representative of a level of the fuel insaid tank.
 16. An apparatus for measuring the volume of a liquid in afuel tank in a vehicle subject to varying external forces caused bymovement or changes in the roll and pitch angles of the vehicle,comprising: a fuel tank mounted to the vehicle and subject to forcesalong the yaw axis of the vehicle; a plurality of SAW pressure sensorsmounted on said tank, each of said SAW pressure sensors providing anoutput signal representative of pressure applied to said SAW pressuresensor by material in an interior of said tank; and processor meanscoupled to said SAW pressure sensors for receiving said output signalsfrom said SAW pressure sensors and for processing said output signals toobtain a volume of fuel in said tank, said processor means comprisingmeans for storing an algorithm representative of a derived relationshipbetween the parameters corresponding to said output signals from saidSAW pressure sensors and the volume of fuel in said tank and applyingthe algorithm using said output signals from said SAW pressure sensorsas input to obtain the volume of fuel in said tank, said algorithm beingobtained by conducting a plurality of measurements, each measurementincluding the known volume of the tank and said output signals from saidSAW pressure sensors.
 17. The apparatus of claim 16, wherein saidplurality of SAW pressure sensors comprises four SAW pressure sensorsarranged each at a different location on a bottom of said tank.
 18. Theapparatus of claim 17, wherein said plurality of SAW pressure sensorsfurther comprises a single SAW pressure sensor arranged at a top of saidtank, said algorithm being obtained to consider output signals from saidSAW pressure sensor arranged at a top of said tank to eliminate effectsof vapor pressure within said tank.
 19. The apparatus of claim 16,wherein said algorithm is a neural network.
 20. A fluid storage tank fora vehicle subject to varying external forces caused by movement orchanges in the roll and pitch angles of the vehicle, comprising acontainer having a sidewall defining in part an interior; and a SAWsensor arranged on said sidewall and including a pressure sensorarranged on an inside of said container and a temperature sensorarranged on an outside of said container, said pressure sensor beingarranged to measure deflection of said sidewall and said temperaturesensor being arranged to measure temperature of the fluid.
 21. A methodfor measuring the volume of a liquid in a fuel tank in a vehicle subjectto varying external forces caused by movement or changes in the roll andpitch angles of the vehicle, comprising the steps of: conducting aplurality of measurements, each measurement including the known volumeof the tank and the value of at least three parameters concerning thetank, at least one of the parameters being the pitch or roll angle ofthe vehicle as determined by an inertial measurement unit (IMU),generating an algorithm from the plurality of measurements fordetermining the volume of fuel in the tank upon the receipt of currentvalues of the parameters, inputting the algorithm into a processorarranged in connection with the vehicle, measuring the same parametersduring operation of the vehicle, and inputting the measured parametersinto the algorithm in the processor such that the algorithm provides thevolume of fuel in the tank.
 22. The method of claim 21, wherein theremaining ones of the parameters is selected from the group consistingof the load of the tank on a load cell arranged at a first location, theload of the tank on a load cell arranged at a second location, the loadof the tank at a load cell arranged at a third location, the height ofthe fuel at a first location in the tank, the height of the fuel at asecond location in the tank and the height of the fuel at a thirdlocation in the tank.